Fiducial alignment masks on microelectronic spring contacts

ABSTRACT

Microelectronic spring contacts with fiducial alignment marks for use on a semiconductor wafer contactor or similar apparatus, and methods for making such marks, are disclosed. Each alignment mark is placed on a pad adjacent to a contact tip. The alignment mark is positioned on the pad so that it will not contact the terminal or any other part of a wafer under test. The alignment mark and the contact tip are preferably positioned on the pad in the same lithographic step. Then, the pad and like pads, selected ones of which also have similar alignment marks, are attached to the ends of an array of resilient contact elements. A plurality of alignment marks in accurate registration with a plurality of contact tips on a contactor is thus disclosed. Configurations for ensuring that the alignment marks remain free of debris and easily located for essentially the entire life of the contactor are disclosed, as are various different exemplary shapes of alignment marks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to components for testing of semiconductordevices, and more particularly to fiducial alignment marks onmicroelectronic contacts for use on probe cards, contactors, and similarcomponents.

2. Description of Related Art

Testing of semiconductor devices, particularly wafer-level testing doneprior to singulation of semiconductor devices from a wafer, isfrequently performed using a component, such as a contactor assemblyhaving a plurality of microelectronic contacts, each of which contacts aterminal pad, solder ball, or other such terminal on the wafer. Becauseof the very fine pitch at which the terminals on the wafer are disposed,and the correspondingly small scale of the microelectronic contactstructures, alignment of contacts and the terminals on the wafer isaccomplished with the help of special alignment machines and methods.

According to one prior art alignment method, at least three alignmentmarks (sometimes called “fiducial” alignment marks) are placed on thewafer at an earlier device manufacturing stage. The position of thesemarks is known with a high degree of accuracy relative to the terminalsor contact pads on the wafer. On the contactor, comparably accuratealignment marks are not present. This has limited the accuracy withwhich certain types of contactors, such as those with tungsten wirecontact elements, can be placed. Tungsten wire contacts cannot be placedon the contactor with a high degree of accuracy, and hence cannot bemaintained in registration with marks on the contactor. However, certainother types of contactors, such as contactors with composite contactshaving lithographically placed contact tip structures as disclosed, forexample, in U.S. Pat. No. 5,864,946 (Eldridge et al.), may be providedwith a plurality of very accurately positioned spring contact tips.

Generally, to be useful as an alignment mark, a mark must be positionedwith an accuracy that is at least one-half the finest pitch (spacing)between adjacent terminals on the wafer. That is, the position of thealignment mark must be known with certainty to be within a sphere havinga diameter no greater than one-half of the pitch of the terminals on thesemiconductor device. For memory devices, many of which have a pitch ofabout 80 micrometers (3.2 mil), an accuracy of at least about 40micrometers (1.6 mil) is accordingly required. Because they are formedduring the same lithographic steps used to create electronic features onthe wafer, wafer alignment marks can be disposed on the wafer with therequired accuracy. Lithographically placed contact tips on some types ofcontactors are also capable of being disposed on the contactor withcomparable accuracy.

According to the prior art alignment method, three or more of theselithographically placed contact tips are selected to serve the functionof alignment marks during a subsequent positioning step. Typically, arelatively small flat area on the distal end of the contact tips is usedas a visual target. These flat areas are relatively easy to see anddistinguish using commonly used vision systems. Using the alignmentmarks on the wafer and the selected contact tips on the contactor asreference points, the wafer and contactor are then positioned relativeto one another so that each of the contact tips on the contactor canmake contact with a corresponding terminal on the wafer. Using thismethod, it is possible to make contact with an array of terminalsdisposed at a very fine pitch.

Although the foregoing alignment method represents advancement overolder methods in that it permits alignment with terminals disposed atpitches down to about 40 micrometers, it suffers from certainlimitations. One limitation is related to the use of spring contact tipsfor alignment of the contactor. During repeated applications of thecontactor, such contact tips can become contaminated with debris (suchas metal oxides or organic residue) from terminals on the wafers undertest. Such debris normally does not interfere with the electricaloperation of the contactor, but can make it difficult to locate theselected contact tips with the requisite degree of accuracy. The targetareas on the contact tips may become obscured or difficult to see. Aseven finer pitches for terminals on semiconductors are tested, and thesize of contact tips shrinks accordingly, this limitation of the priorart method becomes increasingly apparent and costly to overcome. It isdesired, therefore, to provide an apparatus and method that overcomesthe limitations of the prior art method and yet is compatible with theinstalled base of vision and positioning systems.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for providingfiducial alignment marks on a contactor, that overcomes the limitationsof prior art methods. According to an embodiment of the invention, analignment mark is placed on a region or pad adjacent to the contact tip.The alignment mark is positioned on the pad so that it does not contactthe terminal or any other part of the wafer under test, preferably sothat it remains free of debris from the contact tip after repeated useof the contactor. The alignment mark and the contact tip are preferablypositioned on the pad in the same lithographic step. Then, the pad andlike pads, selected ones of which also have similar alignment marks, areattached with the assembled alignment marks and contact tips to the endsof an array of resilient contact elements. A plurality of alignmentmarks in accurate registration with a plurality of contact tips on acontactor may thus be provided. The alignment marks may readily belocated to within an accuracy of at least about 3-5 μm (about 0.1 to 0.2mil), and so may be used in connection with wafers having terminalsdisposed at a pitch as fine as about 20-30 μm (about 0.8 to 1.2 mil).Higher accuracies, such as positioning the alignment marks with anaccuracy of about 1.5 micrometers (0.06 mil), are also believed to beattainable. Furthermore, the alignment marks, including any targetsthereon, may be positioned so as to remain free of debris and,therefore, easily located for essentially the entire life of thecontactor. The alignment marks may be provided in various differentshapes, exemplary ones of which are disclosed herein.

A more complete understanding of the fiducial alignment marks will beafforded to those skilled in the art, as well as a realization ofadditional advantages and objects thereof, by a consideration of thefollowing detailed description of the preferred embodiment. Referencewill be made to the appended sheets of drawings which will first bedescribed briefly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view at very high magnification of acantilever-type microelectronic spring contact having a tip structureaccording to the invention with a co-located contact tip and alignmentmark.

FIG. 2A is a side elevation view of the spring contact shown in FIG. 1.

FIG. 2B is a side elevation view of the tip structure for the springcontact shown in FIG. 1.

FIGS. 3A-3C are plan views of exemplary alternative tip structureshaving co-located contact tips and alignment marks for use with a springcontact.

FIGS. 4A-4B are side elevation and plan views, respectively, of a tipportion of a spring contact, showing a circular-pad type of alignmentmark and an adjacent contact tip.

FIG. 5A is a plan view of an exemplary contactor having a plurality ofmicroelectronic spring contacts, selected ones of which have tipstructures with alignment marks according to the invention.

FIGS. 5C-5D are plan views, at successively higher levels ofmagnification, of the spring contacts and tip structures with alignmentmarks on the exemplary contactor shown in FIG. 5A.

FIG. 5E is a plan view of a tip structure similar to that shown in FIG.5D, having an alternative shape of alignment mark.

FIG. 6 is a perspective view of a sacrificial substrate at an exemplarystep of a process for making a plurality of tip structures like thoseshown in FIGS. 5A-5D.

FIG. 7A is a cross-sectional view of a portion of the sacrificialsubstrate shown in FIG. 6, showing etched features for forming aco-located contact tip and alignment mark in an exemplary step of aprocess for forming a spring contact with an alignment mark according tothe invention.

FIGS. 7B-7D are cross-sectional views of a sacrificial substrate andmaterials layered thereon during exemplary steps of a process forforming a spring contact with an alignment mark according to theinvention.

FIG. 7E is a cross-sectional view showing a spring contact and tipstructure with an alignment mark during an exemplary attachment step.

FIG. 8A is a plan view showing an alternative structure with analignment mark according to the invention and adjacent spring contactshaving relatively small “microtip” contact tips on a contactorsubstrate.

FIG. 8B is a cross-sectional view of the substrate and alternativestructure shown in FIG. 8A.

FIGS. 9A-9D are cross-sectional views of a sacrificial substrate andmaterials layered thereon during exemplary steps of a process forforming recessed alignment marks and adjacent contact tips such as shownin FIG. 8B.

FIGS. 10A-10C are plan views of an exemplary tip structure during stepsof a process for forming an alignment mark using a tool for marking thetip structure after attachment of the contact tip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method and apparatus for providingprecise fiducial alignment marks on microelectronic contacts and oncontactors carrying a plurality of microelectronic contacts. In thedetailed description that follows, like element numerals are used todescribe like elements shown in one or more of the figures.

Referring to FIG. 1, in an embodiment of the invention, an alignmentmark 116 is provided on microelectronic spring structure 100. Springstructure 100 may be configured in various ways as known in the art. Inthe embodiment shown in FIG. 1, spring structure 100 is configured asdisclosed in the commonly-owned, co-pending application Ser. No.09/746,716, filed Dec. 22, 2000, which is incorporated herein byreference, in its entirety. That is, microelectronic spring structure100 comprises a group of column elements or posts 104, a cantileveredbeam 102 secured transverse to the group of column elements, and acontact tip 114 on a portion of the cantilevered beam distal from thecolumn elements. In an alternative embodiment, a lithographicallydeposited post component is used instead of the column elements 104, asdisclosed, for example, in the commonly-owned, co-pending applicationSer. No. 09/023,859, filed Feb. 13, 1998. Additional examples ofsuitable microelectronic spring contacts for use with the presentinvention, and methods for making such contacts, are provided, e.g., bycommonly-owned, co-pending application Ser. No. 09/023,859, filed Feb.13, 1998, Ser. No. 09/364,788, filed Jul. 30, 1999, and Ser. No.09/710,539, filed Nov. 9, 2000, all of which applications areincorporated herein, in their entirety, by reference.

Each of the foregoing applications discloses methods, and the resultingspring structures, for making a microelectronic spring structure bydepositing (such as by electroplating) a resilient material on or in asacrificial layer over a substrate, and then removing the sacrificiallayer. The sacrificial layer may be shaped to have a sloped or contouredregion extending above and away from the substrate, such as byimpressing a moldable (plastic) layer using a specially shaped formingtool to form a mold. In the alternative, or in addition, the sacrificiallayer is patterned to provide openings revealing the substrate below it.A seed layer is deposited over the sacrificial layer and/or exposedregion of the substrate, and patterned in the plan shape of the desiredspring structure or component. The resilient layer is then plated ontothe seed layer. The sacrificial layer is removed, leaving beam, tipand/or post components that are subsequently assembled to providestructures like structure 100. In some embodiments, no assembly isrequired because the deposition/patterning steps provide a springstructure having a base portion attached to the substrate and acontoured and/or sloped beam extending therefrom. However, each of theforegoing structures may include a contact tip that is precisely formedusing a pattern-masking/etching process and assembled to the springcontact structure. Accordingly, the invention may be readily adapted foruse with each of the foregoing structures and methods, and to any otherstructure that provides a similar opportunity for precise formation of acontact tip to a microelectronic contact structure.

As shown in FIG. 1, microelectronic contact structure 100 comprises abeam 102 having an upper surface 108 that serves as a datum surface forattachment of a tip structure 110. To achieve precise planarity ofsurface 108, beam 102 is preferably formed by a lithographic process,for example, by deposition of a resilient material on a sacrificiallayer or substrate as described, e.g., in Ser. No. 09/023,859 referencedabove. As used herein, “sacrificial layer” refers to a material, such asa photoresist, that is deposited on a substrate during formation of adesired component or structure, such as a microelectronic spring contactcomponent, and later removed from the substrate. “Sacrificial substrate”refers to a substrate that is attached to a desired component orstructure, such as a microelectronic spring component, during itsformation, and later removed from the component or structure. So long asstructure 100 provides a datum surface 108 for attachment of a contacttip 114 and/or a tip structure 110, the remaining details of structure100 may be configured in various different ways. For the purpose ofillustrating an exemplary application of the present invention, otherdetails of structure 100 are described below, but it should beappreciated that the invention is not limited thereby.

The beam 102 of structure 100 is secured to substrate 106 by columnelements 104. Substrate 106 comprises a contactor for a semiconductordevice, such as a semiconductor wafer. Such contactors often comprisespecially shaped slabs of ceramic materials having terminals on opposingmajor surfaces and internal electrical traces connecting each terminalon a first surface with a corresponding terminal on a second surface. Inthe alternative, substrate 106 may comprise some other electroniccomponent, such as, for example, a probe card, or other printed circuitboard; a semiconductor device, such as a silicon chip or wafer; aceramic material, or an electrical connector. Column elements 104 aretypically attached to a terminal (not shown) of substrate 106, which isin turn connected to a circuit element of an electronic component, suchas, for example, an interconnect or interposer substrate, asemiconductor wafer or die, a production or test interconnect socket; aceramic or plastic semiconductor package, or chip carrier.

Contact tip 114 is attached to surface 108 of beam 102. In an embodimentof the invention, contact tip 114 is attached to pad (stand-off) 112,which is in turn mounted to surface 108. Together, contact tip 114 andpad 112 comprise tip structure 110. Tip structure 110 further comprisesan alignment mark 116. Pad 112 is used to elevate contact tip 114 abovethe upper surface 108 of beam 102, so that the contact tip contacts aface of a mating electronic component before any other part of structure100. In an alternative embodiment, such as when beam 102 is sloped awayfrom column elements 104 and substrate 106, pad 112 may be omitted, andcontact tip 114 and alignment mark 116 may be attached directly tosurface 108. In both cases, the contact tip 114 and alignment mark 116may be formed on a sacrificial substrate and attached together to beam102, thereby providing precise positioning of the alignment mark withrespect to the contact tip as necessary to provide alignment that is atleast about as accurate as aligning to the contact tip itself.

A side view of structure 100 is shown in FIG. 2A. Contact tip 114 ispreferably located on pad 112 towards columns 104 (i.e., towards thesecured base of beam 102), relative to alignment mark 116, which islocated towards the free end of beam 102. This relative positioninghelps to avoid accumulation of debris on the alignment mark, becausedebris tends to be pushed towards the fixed end (base) of beam 102 whentip 114 is pressed against a mating terminal. Also, positioning thealignment mark towards the free end of the beam helps to avoidinadvertent contact between the alignment mark and a mating substrate,because the free end of the beam tends to be depressed further away fromthe mating substrate than portions closer to its fixed base. Contactwith the mating substrate may damage the mark or cause it to be occludedwith debris, and thus is usually not desirable. However, for someapplications, there may not be sufficient available space to allow forlocating the alignment mark towards the free (distal) end of beam 102.In other cases, the beam may be configured differently so that alocation closer to the distal end is disadvantageous for other reasons.For such applications, the alignment mark 116 may be positioned closerto the fixed base of beam 102, such as shown in plan view in FIG. 3C.

FIG. 2B shows an enlarged side view of the tip structure 110, showingexemplary relative sizes and positions of a contact tip 114 andalignment mark 116 on a pad 112. Contact tip 114 may be a truncatedpyramid shape, having a height “h₁” and a flat surface 118 at its apex.In other embodiments of the invention, the contact tip may be pyramidalwithout a truncated apex, or may be prism-shaped, with or without atruncated tip; or any other suitable shape such as a hemisphere.Pyramids and prisms are commonly used because they are tapered shapescapable of providing a well-supported raised tip, and are readily formedby etching silicon anisotropically along its crystal planes to providepyramidal or prism-shaped pits, and then using the silicon pits as anelectroplating mold. However, the invention is not limited to particularshapes of contact tips.

Similarly, alignment mark 116 may also be prism or pyramidal shaped,because it is advantageous to form the mark 116 on the same sacrificialsubstrate as the contact tip 114 using the same silicon etching andplating technique. To avoid inadvertent contact with a mating component,mark 116 preferably has a height “h₂” that is substantially less than“h₁,” such as, for example, between about one-fourth to three-quartersof “h₁.” The degree of difference between “h₁” and “h₂” may varydepending on the requirements of the application and the geometry of thespring contact. For example, an alignment mark that is placed “inboard”of the contact tip, that is, closer to the fixed end of beam 102, asshown in FIG. 3C, must be relatively short to prevent inadvertentcontact with the mating component and build-up of debris on, thealignment mark. In comparison, an alignment mark “outboard” of thecontact tip, that is, towards the free end of the beam relative to thecontact tip, as shown in FIGS. 2A and 2B, may be somewhat longerrelative to the contact tip. Of course, whatever the relative lengths ofthe contact tip and alignment mark, it is generally preferable that thealignment mark be positioned so as to not contact the mating component,and this will usually mean that the alignment mark be made substantiallyshorter than the contact tip.

Consequently, as shown in FIG. 2B, the width “w” of the alignment markwill generally be less than the width of the contact tip, especiallywhen pyramidal or prism-shaped features are used. At the same time, thewidth of the mark must be at least great enough to be visible on thevision system that will be used to align the contactor that the mark ison. Accordingly, it may be advantageous to increase at least onedimension of the alignment mark, for example, its length, to provide amore readily resolvable feature, while maintaining the height of themark less than the corresponding contact tips.

The prism-shaped alignment mark 116 shown in plan view in FIG. 3Aexemplifies such an approach. Mark 116 may be compared with pyramidalalignment mark 120 shown in plan view in FIG. 3B. Marks 120 and 116 havethe same width “W” and the same height “h₁,” but mark 120 is square inplan view while mark 116 is elongated rectangular in plan view andextends for substantially the width of pad 120. In a vision systemhaving a minimum resolvable feature size about equal to the plan area ofmark 120, the mark will appear as a single pixel or small cluster ofpixels. As such, it may be difficult to distinguish from the surroundingenvironment that may contain irregularities, such as accumulated debrisor oxidation. Such irregularities may appear as single pixels orirregular clusters of pixels, creating a mottled background from whichit may be difficult to discern the alignment mark. By comparison, mark116 will appear as a line of pixels that is much more likely to stand invisual contrast to the surrounding environment. As shown in FIG. 3C, inan embodiment of the invention, alignment mark 116 has a length ‘l1’that is less than the width length ‘l2’ of pad 112 so that an openregion exists at each end of alignment mark 116. A point of the line,such as an endpoint or midpoint, may be selected for use as a referencepoint.

In other embodiments of the invention, a slab-shaped alignment feature,such as a pad, is provided on a contact structure, optionally separatefrom the pad of the contact tip. An exemplary circular slab-shapedalignment pad 126 is shown in FIGS. 4A-4B. Pad 126 is essentially a formof alignment mark produced at a different step of a process for formingmicroelectronic contacts. FIG. 4A shows a side view of the mark 126 andan adjacent tip structure 110 on a tip portion of a spring contact beam102. FIG. 4B shows the same structure in plan view. Such slab-shapedpads shaped and positioned for alignment purposes may be particularlyuseful for certain applications, for example, when there is very limitedavailable height for an alignment mark, when the contact tip 114 isformed by some process other than an etch/plating process, or when arelatively large alignment structure is desired. Alignment pad 126 ispreferably formed and attached to beam 102 in the same process stepswith contact tip pad 112, thereby achieving accurate registration withrespect to contact tip 114. Alignment pad 126 is preferably separate andspaced apart from pad 112, to avoid contamination with debris from tip114 and for greater visibility. Alignment pad 126 also preferably has adistinct shape for greater visibility. A circular shape is particularlypreferred because the center of the circle is readily determined for useas a reference point, while the relatively large circle is readilyvisible. However, any other suitable shape may be used.

FIGS. 5A-5E illustrate application of the foregoing structures to anexemplary contactor. Contactor 130 comprises a generally slab-shapedsubstrate 132, typically a ceramic material. As used herein, “contactor”includes specialized devices for making electrical contact withsemiconductor devices in wafer form during the electrical testing ofsemiconductor devices. In addition, “contactor” may include any otherdevice having a plurality of contact elements, for example, but notlimited to, microelectronic spring contacts, for making contact with anytype of mating component, wherein the contacts on the contactor arealigned with the mating component using a vision system.

As shown in FIG. 5A, a typical contactor may comprise a plurality ofspring contacts 136, that may in turn be arrayed in a plurality ofgroups 138. In an embodiment of the invention, most of the plurality ofspring contacts 136 will not have an alignment mark. A selected few ofthe spring contacts, for example, the four spring contacts 134, areprovided with an alignment mark. The marked contacts 134 are located sothat the position of all of the contacts 136 may be accuratelydetermined from the position of the marked contacts. For manyapplications, at least three or four alignment marks are needed to alignthe contactor. However, additional marked contacts 134 may be providedfor purposes of redundancy; for example, a marked contact may beprovided in each group 138 (not shown). It should be appreciated thatcontactor 130 and contacts 136 are not drawn to scale. Furthermore, forillustrative clarity, contacts 136 are drawn somewhat larger relative tocontactor 130 than may be typical for semiconductor wafer applications.Details of contactor 130, contacts 136, and methods of making thesecomponents, may be as known in the art or as otherwise disclosed in theincorporated references.

FIG. 5B shows an enlarged view of a group of spring contacts 138 oncontactor 130. A typical interleaved arrangement of the spring contacts136 is apparent, as are individual beams 102 and contact tips 114 ofeach spring contact 142. The post or column elements are hidden behindthe beam 102 of each spring contact. Also apparent is adistinctive-shaped pad 140. A relatively large pad, such as pad 140, mayadditionally provide space for a larger alignment mark; or may itselfserve as an alignment mark. The distinctive shape of pad 140 facilitateslocating the marked contactor 134. The pad 140 may be located using avision system at low magnification, because of its relatively large sizeand distinctive shape. Then, magnification of the vision system may beincreased to locate the alignment mark on the contactor 134.

FIG. 5C shows the marked contact 134 and adjacent unmarked contacts 142.The components of unmarked contacts 142 and marked contact 134 are morereadily apparent in this enlarged view. Pad 112, contact tip 114, andbeam 102 of each contact 142 are apparent. Tip 114, pad 140, beam 102,and alignment mark 116 of contact 134 are also apparent. The free end146 and fixed end 148 of the contacts 142, 134 are also indicatedrespectively. In an embodiment of the invention, unmarked contacts 142and marked contacts 134 are provided with the same type of beams 102 andcontact tips 114. However, in alternative embodiments, the markedcontact 134 may use a beam configuration and/or contact tipconfiguration that is different from unmarked contacts 142. For example,in an embodiment of the invention, structure 134 serves only as asupport for an alignment mark, and has no contact tip.

FIG. 5D shows an enlarged view of pad 140 at the free end 146 of beam102. A prism-shape alignment mark 116 is provided on pad 140, aspreviously described with respect to FIGS. 2A-2B. Alternatively, thecircular portion of pad 140 may be used as the aligning feature, andmark 116 may be omitted. Or, more than one alignment mark may beprovided on the same pad 140, for example, two parallel alignment markslike mark 116 may be provided. A cross-shaped mark 144, as shown in FIG.5E, comprised of two crossed prisms, may be particularly helpful forindicating a reference point at the intersection of the cross. Each ofthe foregoing marks may be made using a lithographic mask/etch processas described below.

FIG. 6 shows a perspective view of a sacrificial substrate 150 coveredby a resist layer 152 during an exemplary step of a method for making analignment mark according to the invention. Substrate 150 is typically asilicon substrate and has a planar face extending for a regionpreferably at least as large as the face of the contactor to be providedwith spring contacts. Other substrate materials may be used ifsufficiently uniform and capable of providing a planar surface that maybe uniformly and predictably etched under a patterned resist layer.Resist layer 152 may be any suitable photo-resist material, as known inthe art. Layer 152 is patterned to provide square openings 154 (four ofmany shown) in the positions where contact tips are desired andrectangular openings 156 (one of many shown) where alignment marks aredesired. As should be apparent, a square hole will yield a pyramidal pitwhen the underlying substrate is etched, and a rectangular hole willyield a prism-shaped pit. Other shapes, e.g., crosses, cones, truncatedcones, etc., may be provided by a suitable combination of substrate andopening shape.

FIG. 7A shows a cross-section through exemplary ones of the squareopenings 154 and rectangular openings 156 after etching of substrate152. In an embodiment of the invention, the etching is halted at a pointbefore the pyramidal pit is fully etched. At this point, prism-shapedpit 160, although over-etched, is shallower than pit 158. That is, thedepth of pit 158 is controlled primarily by the time of exposure to theetch solution while the depth of pit 160 is controlled primarily by therelative size of opening 156. After pit 160 is etched to the edge ofopening 156, further etching (“over-etching”), should proceed moreslowly than etching of adjacent pit 158. Production of adjacent pits ofdifferent and controllable depth is thereby achieved.

FIG. 7B shows the same portion of substrate after further processing, asfollows. After the desired pit depths are achieved, etching is haltedand resist layer 152 is removed as known in the art. Typically, aconductive seed and/or release layer 164 is applied over the surface ofthe substrate to facilitate subsequent electroplating and release of thetip structure from substrate 150. Suitable materials for seed and/orrelease layer 164 are known in the art, or are described in theincorporated references. A second resist layer is applied as known inthe art and patterned to reveal a pad-shaped opening 166 forelectroplating a tip structure and support pad for an alignment mark.FIG. 7B shows a single opening disposed over both pits 158 and 156.However, two separate openings (one disposed over each pit 156, 158) maybe provided for forming separate pads, if desired. Furthermore, forembodiments where no raised alignment mark is to be formed, e.g., wherethe alignment mark is pad-shaped, pit 156 may be omitted.

The pad shaped opening 166 is then filled with one or more metalliclayers 168, 170, such as by electroplating, to provide a filled openingas shown in FIG. 7C. The composition of layers 168, 170 is as known inthe art. Any number or composition of layers may be used, and theinvention is not limited thereby. The exposed surface 172 of the topmostlayer 170 may then be planarized, such as by chemical-mechanicalpolishing, and the second resist layer 162 is removed to reveal a tipstructure 110, comprised of a pad 112, a contact tip 114, and analignment mark 116, as shown in FIG. 7D and as previously described. Itshould be apparent that a plurality of similar tip structures, forexample, some with alignment marks like mark 116, others with only oneof a contact tip or alignment mark, and perhaps others with no contacttip or alignment mark at all, will be present on substrate 150, havingtheir exposed surfaces in substantially the same plane. Such tipstructures are then ready for joining to an array of spring contactslike, for example, those shown in FIGS. 5A-5C. It should be appreciatedthat tip structures 110 may take a variety of shapes and are not limitedto the pyramidal shape discussed in the preceding paragraphs.

FIG. 7E shows a cross-section of an exemplary contact structure 134during a step for joining beam 102 to tip structure 110. A joiningmaterial 178, such as a solder paste, is accurately dispensed on surface172, as known in the art. Substrate 150 is placed in a suitable holdingfixture and substrate 106, with a plurality of contact structures inplace on its surface, is lowered in parallel relationship to substrate150 and aligned so that each contact structure, e.g., contact structure134, is aligned with a corresponding tip structure, e.g., structure 110.The substrates are moved together until the joining material contactsboth tip structure 110 and beam 102. The joining material is thenactivated, e.g., by heating, which then pulls the tip structure and beamtogether by surface tension to a relatively uniform position in whichthe material is hardened (such as by cooling). Careful control over thesurface properties of the material to be joined, the amount of joiningmaterial applied per unit area, the alignment of substrates 106 and 150,and curing conditions (such as temperature), will generally yield auniform thickness of bond over the large plurality of tip structuresacross a contactor substrate. The bond thickness affects the accuracywith which the z-position (direction perpendicular to substrate 106) ofthe contact tips and alignment marks are known. The x- and y-positions(positions in a plane parallel to substrate 106) are fixed by thesacrificial substrate and pattern masking steps. Hence, the position ofadjacent tip structures and alignment marks can be determined with therequired accuracy in three dimensions across the substrate. Thepositional accuracy can be confirmed by comparing measured versusexpected positions of selected contact tips across a substrate, relativeto the principal alignment marks. If variances exceed the specifiedtolerance (e.g., ½ the semiconductor device terminal pitch), thesubstrate should be repaired or discarded.

Alignment marks need not be placed on contact structures exactly likethe structures which carry contact tips. The alignment function of themarks may also be realized by placing them on elevated platforms thatare constructed to provide a mounting surface substantially co-planarwith the surfaces to which the contact tips are mounted. The elevatedplatform may be resilient, or supported to be substantially rigid (i.e.,substantially non-resilient). A plan view of a substantially rigidelevated platform 180 adjacent to spring contacts 184 on a substrate 106is shown in FIG. 8A. The configuration shown in FIG. 8A may be desirablein applications which use contact “microtips” 182 on tip structures 194,and correspondingly small contact structures 184. Structures 184 may betoo small to support alignment marks 188, 192. Therefore, an elevatedplatform 180 with a relatively large beam 186 may be provided formounting the alignment marks. Alignment marks 188, 192 may thus beformed on the same sacrificial substrate as microtips 182, andtransferred together with the microtips to structures 180, 184 onsubstrate 106. Registration between the alignment marks and themicrotips is achieved in the same way as previously described.

A side cross-section of platform 180 is shown in FIG. 8B, with portionsof contact structures 184, and especially, tip structures 194, visiblebehind the platform. Pad-type alignment mark 192 has a smooth surfacewithout raised or recessed structures. Recessed alignment marks 188 areprovided in an upper surface of pad 190. Beam 186 is supported along itslength by four columns 104, and is accordingly substantially rigidrelative to cantilevered beams of spring contacts 184.

When the alignment marks are large relative to the contact tips, if maybe preferable to use pad-type marks like mark 192 or recessed marks likemarks 188. Raised alignment marks may be less preferred for suchapplications, because of the small clearance provided by the contacttips. Furthermore, contact tips like microtips 182 may not providesufficient vertical clearance even when the alignment marks are notraised, e.g., pad-type mark 192 and/or marks 188 below the surface ofpad 190. Therefore, it may be further desirable to recess the pad-typemark and pads for alignment marks below the base of the microtips, asshown in FIG. 8B. At the same time, however, the alignment marks and/ortheir pads are preferably formed on the same sacrificial substrate asthe microtips, for the purpose of maintaining accurate registrationbetween the marks and the tips. To achieve the desired structure on thesame sacrificial substrate, a different sequence of manufacturing stepsthan previously described is used.

FIGS. 9A-9F show cross-sectional views of a substrate and materialslayered thereon during steps of an exemplary sequence for makingrelatively large alignment marks adjacent to microtips. The sacrificialsubstrate 200 may be silicon or other etchable material as previouslydescribed. A first resist layer 202 is deposited and patterned to revealmost of the substrate 200 except for directly over where any recessedalignment marks are to be formed. The substrate 200 is then etched toprovide protrusions under the remaining areas of resist 202. The shapeof the protrusions will depend on the etching properties of thesubstrate 200, the etching method employed, and the shape of the resistareas 202. For example, under-etching a rectangular resist area on acrystalline silicon substrate will provide a truncated prism-shapedprotrusion. An exemplary cross-section of two such protrusions 204 isshown in FIG. 9A.

The first resist layer 206 is then stripped and a second resist layer206 is applied and patterned to reveal pad-shaped openings like opening208 where tip structures are to be formed. The substrate is again etchedto provide a plurality of pad-shaped recesses like recess 209 shown inFIG. 9B.

The second resist layer is then stripped, and a third resist layer 210is applied and patterned to provide a plurality of small openings likeopening 212 where contact tips are to be formed. The substrate 200 isagain etched to form a plurality of pyramidal pits like pit 214 shown inFIG. 9C.

The third resist layer is then stripped and a seed/release layer (notshown) is applied. A fourth resist layer (not shown) is applied tosubstrate 200 and patterned to provide pad-shaped openings overprotrusions 204 and pits 214, similarly to as previously described inconnection with FIG. 7B. The substrate is then plated with one or morelayers of metal to substantially fill the openings, and the exposedplated areas are planarized, similarly to as previously described inconnection with FIG. 7C. The fourth resist layer is removed to reveal aplurality of tip structures 194 and recessed alignment marks 188 in pads190, like those shown in FIG. 9D. The tip structures and pads haveplanarized mounting surfaces 216 suitable for joining to a plurality ofcontact structures, similarly to as previously described in connectionwith FIG. 7E. Structures like those shown in FIGS. 8A-8B may thereby beproduced.

It should also be appreciated that the alignment mark may be added tothe tip structure after producing the tip structure, for example, byfurther selective etching or laser marking. Although it is generallypreferable to form the alignment marks in the same lithographic step asthe contact tips, this may not always be possible. For example, it somecases it may be desirable to add alignment marks to a contactor that wasmanufactured without them. The following example exemplifies a methodfor adding alignment marks in a later step.

Referring to FIG. 10A, the pad 300 of tip structure 312 includes acontact tip 314, which may be produced, for example, by one of theprocesses described above. Tip structure 312 may optionally be mountedto a beam 302 of a spring structure. Marking area 304 is provided inwhich the alignment mark is to be placed. In FIG. 10B, a laser markingsystem 324 can be aligned by targeting a low power beam 326 on thecontact tip 314, and then offset a defined distance to a markinglocation 320. The laser 324 may then be fired to emit a higher powerbeam 328 of sufficient power to create a precise mark 316 (shown in FIG.10C). The marking location 316 (target of the laser beam) is offset apredetermined spatial distance, for example, an offset in x, and y anddirections is shown. The offset may additionally include an offset in az-direction (not shown). As shown in FIG. 10C, the mark 316 is definedat the center of the target of the laser beam. Alignment of a contactorusing a subsequently formed mark, such as mark 316, as a reference pointis possible. By way of further example, direct deposition of mark 316can be accomplished using a gas phase organo-metallic precursor and ionbeam direct write. The contact tip 314 is targeted and then the ion beamassisted metal deposition is used to create the features of Mark 316 adefined offset away from the contact tip.

In some embodiments of the invention, the relative position(s) of thecontact tips may be measured and recorded in a data file or database.This data may be obtained from the design process, or measured directlyafter fabrication by optical or other measurement methods. Such data maybe particularly useful for contactors having a plurality of contacts andalignment marks, where the amount of offset between the contact tips ofthe contacts and the alignments marks varies somewhat from contact tocontact across the contactor. Such variations may be more likely tooccur when the alignment marks are not formed in the same lithographicstep as the contact tips, such as, for example, when the alignment marksare formed by laser. To obtain such data, a single point, such as thetip of a contact tip on the contactor, is preferably selected as areference point. It can sometimes be assumed that all of the contacttips are in substantially fixed relation to the reference point, but forprecise positioning, it may be desirable to measure the positions of thecontact tips as well. The position of each alignment mark relative toone or more adjacent contact tips (i.e., the offset) may then bemeasured. From the measured offsets the coordinates of the alignmentmark with respect to the fixed reference point may be determined,irrespective of any variations in offset distances. The coordinate datamay then be input into the test system used to align and place thecontact tips for the testing operation, and thus an optimal alignmentbetween the contactor and the device or wafer to be tested can beobtained.

A method for aligning and contacting corresponding arrays ofmicroelectronic contact elements using alignment marks is exemplified asfollows. The arrays comprise a first array and a second array, and theobject is to achieve contact between corresponding contact elements ofthe first array and of the second array. The contact elements of thefirst array comprise a plurality of contact tips in a substantiallyfixed relationship to the first array, and a plurality of alignmentfeatures. Selected ones of the contact elements of the first array eachfurther comprises an alignment feature spaced apart from a contact tip,as described above. The first array may comprise contact elements of aprobe card, and the second array may comprise contact elements of awafer, but the invention is not limited thereby.

The method comprises, as an initial step, determining coordinates of theplurality of alignment features relative to selected ones of theplurality of contact tips of the first array. This can be accomplishedby direct measurement, or based on a known relationship between elementsformed using a pattern-masking/etch process. The second array ismaintained in a known position, such as by being held in a wafer chuckmounted to the frame of a testing system. The first array is alsomounted in a corresponding movable test head of the testing system. Whenthe arrays are mounted in a suitable testing system, a position of thefirst array relative to the second array is determined by transformingmeasured positions of the plurality of alignment features relative tothe second array using the coordinates. That is, the position of thecontact tips of the first array is determined by measuring the positionof the alignment features and applying a suitable correction based onthe coordinate data. The first array is then positioned relative to thesecond array based on its determined position until contact is achievedbetween corresponding contact elements of the first array and of thesecond array. The position of the contact tips may be repeatedlydetermined as often as desired during the positioning process. Using themethod, the contact tips can be positioned with accuracy to contactcorresponding pads or other contact elements of the second array,without any need to find or measure the location of the contact tipsthemselves during the testing process.

Having thus described a preferred embodiment of fiducial alignment markson microelectronic contacts, it should be apparent to those skilled inthe art that certain advantages of the within system have been achieved.It should also be appreciated that various modifications, adaptations,and alternative embodiments thereof may be made within the scope andspirit of the present invention. For example, a fiducial alignment markon or adjacent to a pad with a contact tip has been illustrated, but itshould be apparent that the inventive concepts described above would beequally applicable to any fiducial mark that is attached to (or formedon) an array of contacts in the same manufacturing step as the contacttips of the array. Furthermore, the inventive concepts would also beapplicable to alignment marks that are placed on other types ofmicroelectronic contacts than shown herein, in registration with, or inmeasured relation to co-located contact tips. For example, alignmentmarks may be placed on membrane probe cards or on contact elements thatare not primarily resilient, such as on buckling-type probes. Similarly,the method of aligning arrays of contact elements using alignment markson contact elements of at least one of the arrays is not limited to usewith a particular type of contactor or device. Rather, the method may beused with any array of contact elements upon which it is possible toplace alignment marks or features in registration or measured relationwith the contact tips or points of such contact elements. The inventionis further defined by the following claims.

1-14. (canceled)
 15. A method for forming a tip structure for amicroelectronic contact, the tip structure comprising an alignment markand a contact tip, said method comprising the steps of: forming thecontact tip and the alignment mark on a sacrificial substrate;transferring the contact tip and the alignment mark to a component of amicroelectronic contact; and removing the sacrificial substrate aftersaid transferring step.
 16. The method according to claim 15, furthercomprising forming the contact tip and the alignment mark by etching thesacrificial substrate through a patterned resist layer to formdepressions therein, and depositing a material in the depressions. 17.The method according to claim 16, further comprising forming a padattached to each of the contact tip and the alignment mark by depositinga material in an opening in a patterned sacrificial layer on thesacrificial substrate, wherein the opening is positioned over thedepressions.
 18. The method according to claim 15, wherein said formingstep further comprises forming the contact tip by etching thesacrificial substrate through a patterned resist layer to form adepression.
 19. The method according to claim 18, further comprisingdepositing a sacrificial layer on the sacrificial substrate after saidforming step, patterning the sacrificial layer to define a first openingtherein positioned over the depression, and depositing a material in thefirst opening to form a pad attached to the contact tip.
 20. The methodaccording to claim 19, further comprising patterning the sacrificiallayer to define at least one second opening, and depositing a materialin the second opening to form the alignment mark adjacent to andseparate from the pad, the alignment mark having a thicknesssubstantially equal to the pad.
 21. The method according to claim 20,further comprising providing the alignment mark with at least onedepression in a surface thereof by defining the at least one secondopening over a protrusion on the sacrificial substrate.
 22. The methodaccording to claim 21, further comprising forming the protrusion priorto said forming the contact tip step by depositing a resist layer on thesacrificial substrate, removing the resist layer except in a locationwhere the protrusion is to be formed, etching the sacrificial substrateto form the protrusion, and removing the resist layer.
 23. A method forforming a contactor having a plurality of microelectronic contacts and aplurality of alignment marks, said method comprising the steps of:providing a contactor substrate having a plurality of microelectroniccontacts thereon; forming the plurality of contact tips and theplurality of alignment marks on a sacrificial substrate; transferringthe plurality of contact tips and the plurality of alignment marks tothe plurality of microelectronic contacts; and removing the sacrificialsubstrate after said transferring step.
 24. The method according toclaim 23, further comprising forming the plurality of contact tips andthe plurality of alignment marks by etching the sacrificial substratethrough a patterned resist layer to form depressions therein, anddepositing a material in the depressions.
 25. The method according toclaim 24, further comprising forming a plurality of pads, one of theplurality of pads attached to each of the plurality of contact tips andto each of the plurality of alignment marks, by depositing a material ina plurality of openings in a patterned sacrificial layer on thesacrificial substrate, wherein each of the plurality of openings ispositioned over at least one of the depressions.
 26. The methodaccording to claim 23, wherein said forming step further comprisesforming the plurality of contact tips by etching the sacrificialsubstrate through a patterned resist layer to form a plurality ofdepressions.
 27. The method according to claim 26, further comprisingdepositing a sacrificial layer on the sacrificial substrate after saidforming step, patterning the sacrificial layer to define a firstplurality of openings therein each positioned over one of the pluralityof depressions, and depositing a material in the first plurality ofopenings to form a plurality of pads each attached to one of theplurality of contact tips.
 28. The method according to claim 27, furthercomprising patterning the sacrificial layer to define a second pluralityof openings, and depositing a material in the second plurality ofopenings to form the plurality of alignment marks adjacent to andseparate from the plurality of pads, the plurality of alignment markshaving a thickness substantially equal to the plurality of pads.
 29. Themethod according to claim 28, further comprising providing at leastselected ones of the plurality of alignment marks with at least onedepression in a surface thereof by defining each of at least selectedones of the second plurality of openings over at least one of aplurality of protrusions on the sacrificial substrate.
 30. The methodaccording to claim 29, further comprising forming the plurality ofprotrusions prior to said forming the plurality of contact tips step bydepositing a resist layer on the sacrificial substrate, removing theresist layer except where ones of the plurality of protrusions are to beformed, etching the sacrificial substrate to form the plurality ofprotrusions, and removing the resist layer.
 31. A method for forming amicroelectronic contact structure, comprising an alignment mark and acontact tip, said method comprising the steps of: forming amicroelectronic contact structure comprising a contact tip attached to asupporting structure; and forming an alignment mark on the supportingstructure a defined offset distance away from the contact tip.
 32. Themethod according to claim 31, wherein the second forming step furthercomprises forming the alignment mark using a laser.
 33. The methodaccording to claim 31, wherein the second forming step further comprisesforming the alignment mark using a ion-beam assisted metal deposition.34. The method according to claim 31, further comprising recordingcoordinates of the defined offset distance relative to the contact tip.35. The method according to claim 31, wherein said first forming stepfurther comprises forming the contact tip on a sacrificial substrate,transferring the contact tip to the supporting structure, and removingthe sacrificial substrate after said transferring step.
 36. The methodaccording to claim 31, wherein said second forming step furthercomprises forming the alignment mark on a sacrificial substrate,transferring the alignment mark to the supporting structure, andremoving the sacrificial substrate after said transferring step.
 37. Themethod according to claim 36, wherein said first forming step furthercomprises forming the contact tip on the sacrificial substrate,transferring the contact tip to the supporting structure, and removingthe sacrificial substrate after said transferring step.
 38. A method foraligning and contacting corresponding arrays of microelectronic contactelements comprising a first array and a second array to achieve contactbetween corresponding contact elements of the first array and of thesecond array, wherein the contact elements of the first array comprise aplurality of contact tips and a plurality of alignment features, andselected ones of the contact elements of the first array each furthercomprises an alignment feature spaced apart from a contact tip, themethod comprising: determining coordinates of the plurality of alignmentfeatures relative to selected ones of the plurality of contact tips ofthe first array; maintaining the second array in a known position;determining a determined position of the first array relative to thesecond array by transforming measured positions of the plurality ofalignment features relative to the second array using the coordinates;positioning the first array relative to the second array using thedetermined position to achieve contact between corresponding contactelements of the first array and of the second array.
 39. The method ofclaim 38, further comprising creating a data file of the coordinates andproviding the data file to a robotic system for aligning the first arraywith the second array.
 40. The method of claim 38, further comprisingmeasuring the measured positions of the plurality of alignment featuresusing a machine vision system.
 41. The method of claim 38, furthercomprising continuously repeating said second determining step duringsaid positioning step.
 42. The method of claim 38, wherein the pluralityof contact tips of the first array are in a substantially fixedrelationship to the first array during the first and second determiningsteps.
 43. A method for aligning an array of contact elements on acontactor with corresponding contact elements on a device, the methodcomprising: forming an alignment feature on at least one of the contactelements on the contactor, wherein the alignment feature is spaced apartfrom a contact tip of the at least one of the contact elements;determining a position of the alignment feature relative to the contacttip; and aligning the contactor with the device using the position ofthe alignment feature.